The present invention relates to a method for testing the operation of a capacitive anti-trap system, as well as a diagnostic device by means of which the operation of a capacitive anti-trap system can be automatically tested.
Capacitive anti-trap systems are provided in the field of automobiles to detect the occurrence of an obstruction in the path of movement of the vehicle closing element during the motor-driven closing of a vehicle closing element such as a side door, tailgate, sunroof or a window, and to prevent this obstruction from being trapped. The occurrence of an obstruction is detected by changing electrical capacitance. For example in the region of the opening in the body to be closed, electrodes are provided on a vehicle structure and/or on the vehicle closing element, said electrodes generating an electrical field in the area of the opening in the body to be closed from the application of an electrical voltage. This electrical field is influenced by the hindrance located in the opening in the vehicle body which changes the electrical capacitance such that an obstacle can be detected by directly or indirectly measuring the electrical capacitance and evaluating a corresponding measuring signal in an electronic evaluation unit. Such an anti-trap protection system is for example known from EP 0 648 628 B1 in conjunction with a motor-driven motor vehicle window.
After an object is detected, normally the adjustment of the vehicle closing element is stopped and/or reversed in order to prevent an obstacle such as a body part of a person from being trapped. The operability of the anti-trap system is accordingly very important. If correct operation of the anti-trap system is not ensured, an obstacle in the adjustment path of the vehicle closing element to be closed cannot be recognized, or at least not with the required reliability, possibly with serious consequences to the health of an individual. There is therefore significant interest in being able to monitor the operability of such an anti-trap system.
In this context, DE 103 10 066 B3 proposes connecting two electrodes of a capacitive anti-trap system by means of an electronic component such as an electrical resistor and applying a test voltage to permanently monitor the operability of the electrodes. In this manner, a short circuit, for example, is immediately detected, and a warning can be output as a reaction.
The solution proposed in DE 103 10 066 B3 is disadvantageous in that a separate electronic component must also be provided, and an independent monitoring process must be implemented in an electronic evaluation unit with its own evaluation logic. Furthermore, the additional electronic component also influences the measuring of the capacitive anti-trap system since additional electronic capacitance is thereby introduced into the system. This influence of the capacitance must be accordingly be taken into account in order to be able to reliably detect the occurrence of an obstacle.